Cleaning liquid, cleaning method, cleaning system, and method for manufacturing microstructure

ABSTRACT

According to embodiments, a cleaning liquid includes an oxidizing substance and hydrofluoric acid and exhibiting acidity. A cleaning method is disclosed. The method includes producing an oxidizing solution including an oxidizing substance by one selected from electrolyzing a sulfuric acid solution, electrolyzing hydrofluoric acid added to a sulfuric acid solution, and mixing a sulfuric acid solution with aqueous hydrogen peroxide. The method includes supplying the oxidizing solution and hydrofluoric acid to a surface of an object to be cleaned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-219890, filed on Sep. 25, 2009; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a cleaning liquid, a cleaning method, a cleaning system and a method for manufacturing a microstructure.

BACKGROUND

Microstructures having fine wall bodies are manufactured on a surface using lithography technology in fields such as semiconductor devices and MEMS (Micro Electro Mechanical Systems). Resists that are formed during manufacturing processes and then become unnecessary are removed using an SPM (sulfuric acid hydrogen peroxide mixture) solution, i.e., a mixed liquid of concentrated sulfuric acid and aqueous hydrogen peroxide (for example, refer to JP-A 2007-123330 (Kokai)).

Oxidizing substances (e.g., peroxomonosulfuric acid) produced by mixing concentrated sulfuric acid and aqueous hydrogen peroxide are included in such an SPM solution.

Further, technology has been proposed to remove the resist adhered to a wafer and the like using oxidizing substances (e.g., peroxomonosulfuric acid) produced by electrolyzing an aqueous solution of sulfuric acid (refer to JP-A 2006-111943 (Kokai)).

The technology discussed in JP-A 2007-123330 (Kokai) and JP-A 2006-111943 (Kokai) decomposes and removes a resist, i.e., an organic substance, using the high oxidative decomposition capability of oxidizing substances that are produced.

Here, while a high-speed operation semiconductor device is manufactured by implanting an impurity with a high dose, an altered layer is formed in the surface of the resist by the implanting of the impurity with the high dose. The resist having such an altered layer formed therein cannot be removed easily; and the desired removal margin unfortunately cannot be obtained only by the oxidative decomposition capability of the oxidizing substances described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a cleaning system according to this embodiment;

FIGS. 2A and 2B are schematic views illustrating the production mechanism of the oxidizing substance;

FIG. 3 is a graph illustrating the effects of the concentration of the oxidizing substances and the concentration of the sulfuric acid on the removal time;

FIG. 4 is a flowchart illustrating the cleaning method;

FIG. 5 is a flowchart illustrating a cleaning method according to another embodiment;

FIG. 6 is a schematic view illustrating a cleaning system in which a sulfuric acid solution having hydrofluoric acid added thereto is electrolyzed; and

FIG. 7 is a schematic view illustrating a cleaning system not provided with a configuration to circulate the solution.

DETAILED DESCRIPTION

In general, according to one embodiment, a cleaning liquid includes an oxidizing substance and hydrofluoric acid and exhibiting acidity.

In another embodiment, a cleaning method is disclosed. The method includes producing an oxidizing solution including an oxidizing substance by one selected from electrolyzing a sulfuric acid solution, electrolyzing hydrofluoric acid added to a sulfuric acid solution, and mixing a sulfuric acid solution with aqueous hydrogen peroxide. The method includes supplying the oxidizing solution and hydrofluoric acid to a surface of an object to be cleaned.

In another embodiment, a cleaning system includes a sulfuric acid electrolysis unit, a sulfuric acid supply unit, a cleaning processing unit, a first hydrofluoric acid supply unit and an oxidizing solution supply unit. The sulfuric acid electrolysis unit includes an anode, a cathode, a partitioning membrane provided between the anode and the cathode, an anode chamber provided between the anode and the partitioning membrane, and a cathode chamber provided between the cathode and the partitioning membrane, the sulfuric acid electrolysis unit electrolyzing a sulfuric acid solution to produce an oxidizing substance in the anode chamber. The sulfuric acid supply unit supplies a sulfuric acid solution to the anode chamber and the cathode chamber. The cleaning processing unit performs a cleaning processing of an object to be cleaned. The first hydrofluoric acid supply unit supplies hydrofluoric acid to the cleaning processing unit. In addition, the oxidizing solution supply unit supplies an oxidizing solution including the oxidizing substance to the cleaning processing unit.

In another embodiment, a cleaning system includes a sulfuric acid electrolysis unit, a sulfuric acid supply unit, a cleaning processing unit, a second hydrofluoric acid supply unit and an oxidizing solution supply unit. The sulfuric acid electrolysis unit includes an anode, a cathode, a partitioning membrane provided between the anode and the cathode, an anode chamber provided between the anode and the partitioning membrane, and a cathode chamber provided between the cathode and the partitioning membrane, the sulfuric acid electrolysis unit electrolyzing a sulfuric acid solution to produce an oxidizing substance in the anode chamber. The sulfuric acid supply unit supplies a sulfuric acid solution to the anode chamber and the cathode chamber. The cleaning processing unit performs a cleaning processing of an object to be cleaned. The second hydrofluoric acid supply unit supplies hydrofluoric acid to the anode chamber. In addition, the oxidizing solution supply unit supplies an oxidizing solution including the oxidizing substance to the cleaning processing unit.

In another embodiment, a method is disclosed for manufacturing a microstructure. The method includes cleaning an object to be cleaned by the above cleaning method and forming a microstructure.

Embodiments will now be described with reference to the drawings. Similar components in the drawings are marked with like reference numerals, and a detailed description is omitted as appropriate.

FIG. 1 is a schematic view illustrating a cleaning system according to this embodiment.

As illustrated in FIG. 1, a cleaning system 5 includes a sulfuric acid electrolysis unit 10, a hydrofluoric acid supply unit 50, a cleaning processing unit 12, a solution circulation unit 14, and a sulfuric acid supply unit 15.

The sulfuric acid electrolysis unit 10 has a function of electrolyzing a sulfuric acid solution and producing an oxidizing substance in an anode chamber 30. Although the oxidizing capability of a solution including oxidizing substances decreases when the solution including oxidizing substances is used to remove contaminants (e.g., deposits such as a resist, metal impurities, particles, dry etching residue, silicon oxide, halides, etc.) adhered to an object to be cleaned, the sulfuric acid electrolysis unit 10 has a function of recovering the reduced oxidizing capability.

The sulfuric acid electrolysis unit 10 includes an anode 32, a cathode 42, a partitioning membrane 20 provided between the anode 32 and the cathode 42, the anode chamber 30 provided between the anode 32 and the partitioning membrane 20, and a cathode chamber 40 provided between the cathode 42 and the partitioning membrane 20.

An upper end sealing unit 22 is provided at the upper end of the partitioning membrane 20, the anode chamber 30, and the cathode chamber 40; and a lower end sealing unit 23 is provided at the lower end of the partitioning membrane 20, the anode chamber 30, and the cathode chamber 40. The anode 32 opposes the cathode 42 with the partitioning membrane 20 interposed therebetween. The anode 32 is supported by an anode support body 33; and the cathode 42 is supported by a cathode support body 43. A direct-current power source 26 is connected between the anode 32 and the cathode 42.

The anode 32 is made of a conductive anode base member 34 and an anode conductive film 35 formed on a surface of the anode base member 34. The anode base member 34 is supported by the inner face of the anode support body 33; and the anode conductive film 35 faces the anode chamber 30.

The cathode 42 is made of a conductive cathode base member 44 and a cathode conductive film 45 formed on a surface of the cathode base member 44. The cathode base member 44 is supported by the inner face of the cathode support body 43; and the cathode conductive film 45 faces the cathode chamber 40.

An anode inlet 19 is formed on the lower end side of the anode chamber 30; and an anode outlet 17 is formed on the upper end side. The anode inlet 19 and the anode outlet 17 communicate with the anode chamber 30. A cathode inlet 18 is formed on the lower end side of the cathode chamber 40; and a cathode outlet 16 is formed on the upper end side. The cathode inlet 18 and the cathode outlet 16 communicate with the cathode chamber 40.

The hydrofluoric acid supply unit 50 includes a tank 51 that retains an aqueous solution of hydrogen fluoride (HF), i.e., hydrofluoric acid, a pump 52, and an open/shut valve 71. The tank 51, the pump 52, and the open/shut valve 71 are connected to a dispense unit 61 via a piping line 53 and a piping line 74. The hydrofluoric acid retained in the tank 51 can be supplied to the dispense unit 61 via the piping line 53 and the piping line 74 by the operation of the pump 52. In other words, the hydrofluoric acid supply unit 50 has a function of supplying the hydrofluoric acid retained in the tank 51 to the dispense unit 61 of the cleaning processing unit 12; and the hydrofluoric acid supplied to the dispense unit 61 can be supplied to the surface of an object W to be cleaned. Hydrofluoric acid also can be supplied to the object W to be cleaned from a piping system separate from that of the solution including oxidizing substances (the oxidizing solution) by providing a not-illustrated piping line and dispense unit separate from the piping line 74 and the dispense unit 61.

The cleaning processing unit 12 has a function of cleaning the object W to be cleaned using the solution including oxidizing substances (the oxidizing solution) obtained in the sulfuric acid electrolysis unit 10 and the hydrofluoric acid supplied by the hydrofluoric acid supply unit 50.

The oxidizing solution obtained in the sulfuric acid electrolysis unit 10 is supplied to the dispense unit 61 provided in the cleaning processing unit 12 via the solution circulation unit 14. The hydrofluoric acid is supplied by the hydrofluoric acid supply unit 50 to the dispense unit 61 provided in the cleaning processing unit 12. The oxidizing solution and the hydrofluoric acid may be supplied sequentially; and the oxidizing solution and the hydrofluoric acid may be supplied substantially simultaneously.

The oxidizing solution and the hydrofluoric acid may be mixed; and the mixed liquid (the cleaning liquid) may be supplied. In the case where the hydrofluoric acid supplied by the hydrofluoric acid supply unit 50 and the oxidizing solution supplied by the sulfuric acid electrolysis unit 10 are supplied substantially simultaneously to the piping line 74, the piping line 74 forms a mixing unit mixing both solutions.

Also, a not-illustrated tank may be provided to mix the oxidizing solution and the hydrofluoric acid. In such a case, the not-illustrated tank forms a mixing unit. By providing the not-illustrated tank, the flow rate fluctuation of the mixed liquid (the cleaning liquid) can be buffered, the mixing rate can be adjusted, etc. Also, the properties of the mixing rate of the mixed liquid (the cleaning liquid) can be made more uniform.

The dispense unit 61 has a dispensing nozzle for dispensing the oxidizing solution, the hydrofluoric acid, and the mixed liquid (the cleaning liquid) of the oxidizing solution and the hydrofluoric acid onto the object W to be cleaned. A rotating table 62 is provided on which the object W to be cleaned is placed to oppose the dispensing nozzle. The rotating table 62 is provided in the interior of a cover 29. By dispensing the oxidizing solution, the hydrofluoric acid, and the mixed liquid (the cleaning liquid) of the oxidizing solution and the hydrofluoric acid from the dispense unit 61 toward the object W to be cleaned, the contaminants (e.g., deposits such as the resist, metal impurities, particles, dry etching residue, silicon oxide, halides, etc.) can be removed from the top of the object W to be cleaned. The removing of the contaminants from the top of the object W to be cleaned is described below.

Although so-called single wafer processing is used in the cleaning processing unit 12 illustrated in FIG. 1, batch processing also may be used.

The oxidizing solution produced in the sulfuric acid electrolysis unit 10 is supplied from the anode outlet 17 to the cleaning processing unit 12 via the solution circulation unit 14. As a solution maintaining unit, the anode outlet 17 is connected to a tank 28 via a piping line 73 in which an open/shut valve 73 a is provided. The tank 28 is connected to the dispense unit 61 via the piping line 74. The oxidizing solution retained in the tank 28 is supplied to the dispense unit 61 via the piping line 74 by the operation of a pump 81. An open/shut valve 74 a is provided in the piping line 74 on the dispensing side of the pump 81. In this embodiment, the tank 28, the pump 81, etc., form an oxidizing solution supply unit that supplies the oxidizing solution including oxidizing substances to the cleaning processing unit 12. In such a case, the flow rate fluctuation of the oxidizing solution produced in the sulfuric acid electrolysis unit 10 can be buffered by retaining and maintaining the oxidizing solution in the tank 28. Temperature control of the oxidizing solution can be performed by providing the tank 28 with a heater.

The oxidizing solution discharged from the cleaning processing unit 12 can be recovered by the solution circulation unit 14 and is resuppliable to the cleaning processing unit 12. For example, the oxidizing solution discharged from the cleaning processing unit 12 is suppliable to the anode inlet 19 of the sulfuric acid electrolysis unit 10 by passing through a returning tank 63, a filter 64, a pump 82, and an open/shut valve 76 in this order. In other words, the oxidizing solution may be circulated between the sulfuric acid electrolysis unit 10 and the cleaning processing unit 12. In such a case, as necessary, the oxidizing solution used during the cleaning processing can be supplied to the sulfuric acid electrolysis unit 10; subsequently, the oxidizing solution including oxidizing substances obtained by performing electrolysis in the sulfuric acid electrolysis unit 10 can be passed through the tank 28, etc.; and the oxidizing solution can be supplied to the cleaning processing unit 12.

Here, as necessary, the oxidizing solution can be produced by supplying diluted sulfuric acid from the sulfuric acid supply unit 15 to the sulfuric acid electrolysis unit 10 as well as supplying the used oxidizing solution to the sulfuric acid electrolysis unit 10, and then performing electrolysis. The oxidizing solution obtained here can be passed through the tank 28, etc., and supplied to the cleaning processing unit 12. By repeating such re-utilization of the oxidizing solution as much as possible, it is possible to reduce the amount of the materials (chemical solutions, etc.) necessary to produce the oxidizing solution and the amount of the waste fluid during the cleaning processing of the object W to be cleaned.

Alternatively, the oxidizing solution discharged from the cleaning processing unit 12 is suppliable to the tank 28 by passing through the returning tank 63, the filter 64, the pump 82, and an open/shut valve 91 in this order, that is, without passing through the sulfuric acid electrolysis unit 10. Here, continuing, cleaning processing of the object W to be cleaned can be performed by supplying the oxidizing solution from the tank 28 to the cleaning processing unit 12. In such a case, the oxidizing solution after use in the cleaning processing can be re-utilized. By repeating such re-utilization of the oxidizing solution as much as possible, it is possible to reduce the amount of the materials (chemical solutions, etc.) necessary to produce the oxidizing solution and the amount of the waste fluid.

The hydrofluoric acid and the mixed liquid (the cleaning liquid) of the oxidizing solution and the hydrofluoric acid discharged from the cleaning processing unit 12 also can be circulated and re-utilized similarly. A not-illustrated returning tank, open/shut valve, etc., can be connected to the cleaning processing unit 12 for the hydrofluoric acid to separate and recover the hydrofluoric acid and the oxidizing solution. In such a case, by supplying the hydrofluoric acid and the oxidizing solution sequentially, the separation and recovery can be performed during each supplying. Separate re-utilization is possible by separate reprocessing, etc.

The returning tank 63 is provided with a discharge piping line 75 and a discharge valve 75 a having a function of discharging the contaminants cleaned and removed in the cleaning processing unit 12 to the outside of the system. The filter 64 has a function of filtering the contaminants included in the oxidizing solution, the hydrofluoric acid, and the mixed liquid (the cleaning liquid) discharged from the cleaning processing unit 12.

The sulfuric acid supply unit 15 has a function of supplying a dilute sulfuric acid solution to the sulfuric acid electrolysis unit 10 (the anode chamber 30 and the cathode chamber 40). The sulfuric acid supply unit 15 includes a pump 80 which supplies the dilute sulfuric acid solution to the anode chamber 30 and the cathode chamber 40, a tank 60 which retains the dilute sulfuric acid, and open/shut valves 70 and 72.

A dilute sulfuric acid solution having, for example, a sulfuric acid concentration not less than 30 weight percent and not more than 70 weight percent is retained in the tank 60. The pump 80 is driven such that the sulfuric acid solution in the tank 60 passes through the open/shut valve 70 and is supplied to the anode chamber 30 via the piping line on the downstream side of the open/shut valve 76 and the anode inlet 19. Also, the pump 80 is driven such that the sulfuric acid solution in the tank 60 passes through the open/shut valve 72 and is supplied to the cathode chamber 40 via a piping line 86 on the downstream side of the open/shut valve 72 and the cathode inlet 18.

In this embodiment, damage of the partitioning membrane 20 due to the electrolysis of the sulfuric acid can be suppressed because the sulfuric acid concentration of the solution supplied to the cathode side is low. In other words, water on the cathode side moves to the anode side during the electrolysis reaction of the sulfuric acid; the sulfuric acid concentration of the solution on the cathode side increases; and the partitioning membrane 20 easily deteriorates. Moreover, in the case where an ion exchange membrane is used as the partitioning membrane 20, the resistance of the ion exchange membrane increases as the water content decreases in the concentrated sulfuric acid; and the tank voltage undesirably increases. Therefore, to mitigate such problems as well, the resistance increase can be suppressed by supplying dilute sulfuric acid to the cathode side to supply water to the ion exchange membrane.

By reducing the concentration of the sulfuric acid supplied to the sulfuric acid electrolysis unit 10, the production efficiency of the oxidizing substances (e.g., peroxomonosulfuric acid and peroxodisulfuric acid) included in the oxidizing solution can be increased. Increasing the production efficiency of the oxidizing substance is described below.

The open/shut valves 70, 71, 72, 73 a, 74 a, 75 a, 76, and 91 described above also have a function of controlling the flow rate of the various solutions. The pumps 80, 81, and 82 also have a function of controlling the flow velocities of the various solutions.

From the aspect of chemical resistance, the material of the anode support body 33, the cathode support body 43, the cathode outlet 16, the anode outlet 17, the cathode inlet 18, the anode inlet 19, and the cover 29 of the cleaning processing unit 12 may favorably include, for example, a fluorocarbon resin such as polytetrafluoroethylene.

The piping that supplies the oxidizing solution, the hydrofluoric acid, and the mixed liquid (the cleaning liquid) of the oxidizing solution and the hydrofluoric acid to the cleaning processing unit 12 may include a fluorocarbon resin tube wound with insulation, etc. Such piping also may be provided with in-line heaters made of fluorocarbon resin. The pumps that pump the oxidizing solution, the hydrofluoric acid, and the mixed liquid (the cleaning liquid) of the oxidizing solution and the hydrofluoric acid may include a bellows pump made of fluorocarbon resin having heat resistance and chemical resistance.

The material of the tanks that retain the sulfuric acid solution may include, for example, quartz. The material of each of the tanks that retain the hydrofluoric acid and the mixed liquid (the cleaning liquid) of the oxidizing solution and the hydrofluoric acid may include, for example, fluorocarbon resin. Each of the tanks also may include an overflow control device, temperature control device, etc., as appropriate.

Here, the processing time can be shortened by increasing the solution temperature (the processing temperature) by providing the tank with a temperature control device, providing the piping with an in-line heater, etc., to increase the reactivity with the resist, etc. However, increasing the temperature too high may cause problems regarding the allowable temperature and strength of the components of the cleaning system (e.g., the piping lines, open/shut valves, pumps, and tanks of each unit, the cover of the cleaning processing unit, etc.). The components often are formed of, for example, fluorocarbon resin, etc., to increase the chemical resistance of the portions in contact with the hydrofluoric acid, the sulfuric acid, and the oxidizing solution. In such a case, the necessary strength may not be obtainable in the case where the temperature is too high.

Therefore, considering shortening the processing time and the allowable temperature, strength, etc., of the cleaning system, it is favorable for the temperatures of the hydrofluoric acid, the sulfuric acid, and the oxidizing solution to be not less than 100° C. and not more than 110° C.

The partitioning membrane 20 may include, for example, a neutral film (albeit having undergone hydrophillizing processing) including a PTFE porous partitioning membrane such as that having the product name Poreflon, etc., and a positive ion exchange membrane such as those having the product names Nafion, Aciplex, Flemion, etc. The dimensions of the partitioning membrane 20 are, for example, about 50 square centimeters. It is suitable for the upper end sealing unit 22 and the lower end sealing unit 23 to include, for example, an O ring coated with fluorocarbon resin.

The material of the anode conductive base member 34 may include, for example, p-type silicon and valve metal such as niobium. Herein, “valve metal” refers to a metal having the metal surface thereof uniformly covered with an oxide film by anode oxidation and having excellent corrosion resistance. The cathode conductive base member 44 may include, for example, n-type silicon.

The material of the anode conductive film 35 and the cathode conductive film 45 may include, for example, glassy carbon. From the aspect of durability, it is suitable to use a conductive diamond film in the case where a solution having a relatively high sulfuric acid concentration and a solution to which hydrofluoric acid is added are supplied.

For both the anode and the cathode, the conductive film and the base member may be formed of the same material. For example, in the case where glassy carbon is used as the cathode base member and in the case where a conductive diamond self-supporting film is used as the anode base member, the base member itself forms a conductive film having electrocatalytic properties which can contribute to the electrolyzing reaction.

Although diamond has stable chemical, mechanical, and thermal properties, it has been difficult to use diamond in an electrochemical system because of poor conductivity. However, a conductive diamond film can be obtained by forming a film while supplying boron gas and nitrogen gas using hot filament chemical vapor deposition (HF-CVD). The conductive diamond film has a wide potential window of, for example, 3 to 5 volts and an electrical resistance of, for example, 5 to 100 milli-ohm-centimeters.

Here, the potential window is the minimum potential (not less than 1.2 volts) necessary for the electrolysis of water. The potential window differs by material qualities. In the case where a material having a wide potential window is used and electrolysis is performed at a potential inside the potential window, an electrolyzing reaction having an oxidation-reduction potential inside the potential window may progress preferentially to the electrolysis of water; and there are cases where the oxidation reaction or reduction reaction of a substance which does not easily electrolyze can progress preferentially. Accordingly, decomposing and synthesizing is possible by using such a conductive diamond for substances which cannot undergo conventional electrochemical reactions.

In HF-CVD, decomposition is performed by supplying the source-material gas to the tungsten filament in a high-temperature state. The radicals necessary for forming the film are formed. Subsequently, the radicals diffused into the substrate surface react with other reactive gases to form the film on the desired substrate.

The production mechanism of the oxidizing substance in the sulfuric acid electrolysis unit 10 will now be described.

FIGS. 2A and 2B are schematic views illustrating the production mechanism of the oxidizing substance. FIG. 2A is a schematic side cross-sectional view of the sulfuric acid electrolysis unit. FIG. 2B is a schematic view illustrating the cross section along line A-A of FIG. 2A.

As illustrated in FIGS. 2A and 2B, the anode 32 and the cathode 42 are provided to oppose each other with the partitioning membrane 20 interposed therebetween. The anode 32 is supported by the anode support body 33 with the anode conductive film 35 of the anode 32 facing the anode chamber 30. The cathode 42 is supported by the cathode support body 43 with the cathode conductive film 45 of the cathode 42 facing the cathode chamber 40. Electrolysis unit housings 24 are provided on both end portions of each of the partitioning membrane 20, the anode support body 33, and the cathode support body 43.

A sulfuric acid solution (a dilute sulfuric acid solution) of 70 weight percent, for example, is supplied from the tank 60 to the anode chamber 30 via the anode inlet 19. The 70 weight percent sulfuric acid solution (the dilute sulfuric acid solution), for example, is supplied from the tank 60 also to the cathode chamber 40 via the cathode inlet 18.

By applying a positive voltage to the anode 32 and a negative voltage to the cathode 42, an electrolysis reaction occurs in each of the anode chamber 30 and the cathode chamber 40. The reactions of chemical formula 1, chemical formula 2, and chemical formula 3 occur in the anode chamber 30.

2HSO₄ ⁻→S₂O₈ ²⁻+2H⁺+2e ⁻  Chemical formula 1

HSO₄ ⁻+H₂O→HSO₅ ⁻+2H⁺+2e ⁻  Chemical formula 2

2H₂O→4H⁺+4e ⁻+O₂↑  Chemical formula 3

Here, the water (H₂O) in chemical formula 2 and chemical formula 3 is the water included as 30 percent of the 70 weight percent sulfuric acid solution. In the anode chamber 30, the reaction of chemical formula 2 produces peroxomonosulfuric acid ions (HSO₅ ⁻). The overall reaction of chemical formula 4 occurs by the elementary reactions of chemical formula 1 and chemical formula 3 to produce peroxomonosulfuric acid ions (HSO₅ ⁻) and sulfuric acid. Peroxomonosulfuric acid has a cleaning capability higher than that of sulfuric acid.

S₂O₈ ²⁻+H⁺+H₂O→HSO₅ ⁻+H₂SO₄  Chemical formula 4

Alternatively, in some cases, the peroxomonosulfuric acid ions (HSO₅ ⁻) of chemical formula 4 are produced after hydrogen peroxide (H₂O₂) is produced as illustrated by chemical formula 5 from the elementary reactions of chemical formula 1 and chemical formula 3. In some cases, peroxodisulfuric acid (H₂S₂O₈) is produced by the reaction of chemical formula 1. Chemical formula 4 and chemical formula 5 are second order reactions from chemical formula 1.

S₂O₈ ²⁻+H⁺+H₂O→H₂O₂+H₂SO₄  Chemical formula 5

Hydrogen gas is produced in the cathode chamber 40 as illustrated by chemical formula 6. This occurs because hydrogen ions (H⁺) produced at the anode move to the cathode via the partitioning membrane 20 and an electrolysis reaction occurs. The hydrogen gas is discharged from the cathode chamber 40 via the cathode outlet 16.

2H⁺+2e ⁻→H₂↑  Chemical formula 6

In this embodiment as illustrated by chemical formula 7, oxidizing substances such as, for example, peroxomonosulfuric acid (H₂SO₅), peroxodisulfuric acid (H₂S₂O₈), etc., can be obtained by electrolyzing the sulfuric acid solution; and an oxidizing solution including these oxidizing substances can be obtained. Although hydrogen gas is produced as a by-product, the hydrogen gas does not affect the removal of the resist, etc.

H₂SO₄+H₂O→oxidizing substances+H₂  Chemical formula 7

In the case where peroxomonosulfuric acid is used, the reaction rate with organic substances such as the resist is high. Therefore, even the resist removal, in which the amount to be removed is relatively large, can be completed in a short length of time. Also, in the case where peroxomonosulfuric acid is used, removal is possible at a low temperature. Therefore, the fine-tuning time for temperature ramp-up and the like is unnecessary. Moreover, peroxomonosulfuric acid can be produced stably in large amounts. Therefore, the reaction rate with the object of removal can be increased even at low temperatures.

Here, to increase the production efficiency by shortening the processing time, it is sufficient to increase the amount of the oxidizing substance. In such a case, the amount of oxidizing substance produced can be increased by increasing the apparatus size, increasing the applied power, increasing the amount of the dilute sulfuric acid solution, etc. However, such actions lead to higher production costs and environmental impacts. Therefore, it is necessary to efficiently produce the oxidizing substance by increasing the electrolysis efficiency.

According to knowledge obtained by the inventors, in the case of constant electrolysis parameters (e.g., the amount of electricity, flow rate, temperature, etc.), more oxidizing substances are produced by reducing the sulfuric acid concentration during the electrolyzing. Therefore, the production efficiency of the oxidizing substances (e.g., peroxomonosulfuric acid and peroxodisulfuric acid) included in the oxidizing solution can be increased by reducing the sulfuric acid concentration supplied to the sulfuric acid electrolysis unit 10.

FIG. 3 is a graph illustrating the effects of the concentration of the oxidizing substances and the concentration of the sulfuric acid on the peeling time (the removal time). The oxidizing substance concentration is plotted on the horizontal axis. The peeling time (the removal time) is plotted on the vertical axis. In FIG. 3, B1 is the case where the sulfuric acid concentration is 70 weight percent; B2 is the case where the sulfuric acid concentration is 80 weight percent; B3 is the case where the sulfuric acid concentration is 85 weight percent; B4 is the case where the sulfuric acid concentration is 90 weight percent; and B5 is the case where the sulfuric acid concentration is 95 weight percent.

FIG. 3 shows that as the sulfuric acid concentration is reduced, more oxidizing substances are produced and the concentration of the oxidizing substances therefore increases. Also, for the same sulfuric acid concentration, the peeling time (the removal time) shortens as the concentration of the oxidizing substances increases (as the amount of the oxidizing substances increases).

In other words, more oxidizing substances can be produced as the sulfuric acid concentration is reduced in the production stage of the oxidizing substances. As a result, the peeling time (the removal time) can be shortened.

Therefore, in this embodiment, a dilute sulfuric acid solution having a sulfuric acid concentration not less than 30 weight percent and not more than 70 weight percent is supplied to the sulfuric acid electrolysis unit 10.

Therefore, more oxidizing substances can be produced by increasing the electrolysis efficiency of the sulfuric acid electrolysis unit 10. As a result, an oxidizing solution including a large amount of oxidizing substances can be supplied to the surface of the object W to be cleaned. Therefore, the processing time can be shortened.

Here, while a high-speed operation semiconductor device is manufactured by implanting an impurity with a high dose, an altered layer is formed in the surface of the resist by the implanting of the impurity with the high dose. The resist having such an altered layer formed therein is not removed easily; and the desired removal margin unfortunately cannot be obtained only by the oxidative decomposition capability of the oxidizing substances described above.

In such a case, it is conceivable to remove the resist having the altered layer formed in the surface thereof by using a substance having a decomposition capability and a removal capability higher than those of oxidizing substances. For example, hydrofluoric acid, which is used to remove oxide films and native oxide films, has a high decomposition capability and a high removal capability. Therefore, it is conceivable to use hydrofluoric acid to remove the resist having the altered layer formed in the surface thereof.

However, the hydrofluoric acid used to remove oxide films and native oxide films has the capability to decompose and remove oxides (e.g., silicon oxide films, etc.) and nitrides (e.g., silicon nitride films, etc.). Therefore, the oxide films and nitride films formed on the wafer may undesirably be removed; and so-called film reduction may occur. In particular, such portions may be undesirably removed in the case where oxide films, nitride films, and the like are exposed at portions not covered with the resist.

Therefore, hydrofluoric acid had been considered unusable in applications having the object of removing an organic substance such as a resist.

As a result of investigations of the inventors, knowledge was obtained that the removal capability of hydrofluoric acid in an acidic solution including oxidizing substances on oxides (e.g., a silicon oxide film, etc.) and nitrides (e.g., a silicon nitride film, etc.) can be suppressed. Knowledge was obtained also that in such a case, even though the capability to remove oxides and nitrides is suppressed, the capability to remove the resist can be increased by including hydrofluoric acid.

Table 1 compares the capability to remove an oxide film, a nitride film, and a resist having an altered layer formed therein.

A silicon oxide film (SiO₂) was formed on a silicon substrate by a thermal oxide film method to form the oxide film. A silicon nitride film (SiN) was formed on a silicon substrate by LP-CVD to form the nitride film. To form the resist having the altered layer formed therein, a resist was coated on a silicon substrate, exposed, developed, and patterned; and the resist surface was altered by a 10¹⁶ atoms/cm² dose of arsenic.

An SPM solution was produced by mixing a sulfuric acid solution having a sulfuric acid concentration of 98 weight percent with aqueous hydrogen peroxide having a hydrogen peroxide concentration of 35 weight percent in a volume ratio of 3:1 (sulfuric acid solution:aqueous hydrogen peroxide=3:1). In such a case, mixing the sulfuric acid solution and the aqueous hydrogen peroxide produces oxidizing substances (e.g., peroxomonosulfuric acid (H₂SO₅), peroxodisulfuric acid (H₂S₂O₈), etc.). Therefore, the SPM solution also is an oxidizing solution including oxidizing substances.

The oxidizing solution including the oxidizing substances was produced by electrolyzing a dilute sulfuric acid solution having a sulfuric acid concentration of 70 weight percent.

The aqueous solution of hydrofluoric acid was made by adding hydrofluoric acid to water to form an aqueous solution having a hydrofluoric acid concentration of 1000 ppm.

The sulfuric acid solution to which hydrofluoric acid was added was made by adding hydrofluoric acid to a sulfuric acid solution having a sulfuric acid concentration of 98 weight percent to provide a hydrofluoric acid concentration of 1000 ppm.

The oxidizing solution to which hydrofluoric acid was added was made by adding hydrofluoric acid to a solution produced by electrolyzing a dilute sulfuric acid solution having a sulfuric acid concentration of 70 weight percent to obtain a hydrofluoric acid concentration of 1000 ppm.

The removal of the oxide film (the silicon oxide film, i.e., SiO₂) and the nitride film (the silicon nitride film, i.e., SiN) was evaluated by the etching rates; and the etching amounts were measured for a processing time of 3 minutes at a processing temperature of 60° C.

The removal of the resist having the altered layer formed therein was evaluated by observation with the naked eye. The processing temperature when removing the resist having the altered layer formed therein was 80° C. in the case where the aqueous solution of hydrofluoric acid was used and 130° C. in the case where other solutions were used.

TABLE 1 ETCHING PEELING RATE CONDITION OF (A/3 min) RESIST HAVING SiO₂ SiN ALTERED LAYER SPM SOLUTION 0 0 PEELING REMNANTS EXIST OXIDIZING SOLUTION 0 0 PEELING PRODUCED BY REMNANTS EXIST ELECTROLYZING SULFURIC ACID AQUEOUS SOLUTION HAVING 22 31 NOT PEELED HYDROFLUORIC ACID CONCENTRATION OF 1000 PPM SURFURIC ACID SOLUTION 21 13 NOT PEELED HAVING HYDROFLUORIC ACID CONCENTRATION OF 1000 PPM OXIDIZING SOLUTION HAVING 0 5 PEELED WITHOUT HYDROFLUORIC ACID PEELENG CONCENTRATION OF 1000 PPM REMNANTS

As illustrated in table 1, the silicon oxide film (SiO₂) and the silicon nitride film (SiN) were not removed in the case where only the SPM solution (the oxidizing solution including the oxidizing substances produced by mixing the sulfuric acid solution and aqueous hydrogen peroxide) was used and in the case where only the oxidizing solution including the oxidizing substances produced by electrolyzing the dilute sulfuric acid solution was used. In other words, the silicon oxide film (SiO₂) and the silicon nitride film (SiN) were not damaged in the case where only the oxidizing solution including the oxidizing substances was used to remove an organic substance such as a resist. However, when removing a resist having an altered layer formed in the surface thereof, the resist was not completely removed and so-called peeling remnants (residue) were left.

There is a risk that yields may markedly decrease in the case where such peeling remnants (residue) remain through the processing of the next process. Although it is conceivable to address such problems by using more stringent dry etching conditions in previous processes and performing other chemical solution processing, the costs increase and new problems such as oxidization of the wafer may occur.

In the case where the aqueous solution having the hydrofluoric acid concentration of 1000 ppm was used, the silicon oxide film (SiO₂) and the silicon nitride film (SiN) were etched and undesirably removed. In other words, there is a risk of damage to the silicon oxide films (SiO₂) and the silicon nitride films (SiN) in the case where an organic substance such as a resist is removed using only a hydrofluoric acid aqueous solution.

According to experiments performed by the inventors, it was ascertained that a resist having an altered layer formed in the surface thereof cannot be removed in the case where an aqueous solution of hydrofluoric acid is used. In other words, it was ascertained that the aqueous solution of hydrofluoric acid is unsuitable for removing the resist.

In the case where hydrofluoric acid was added to the sulfuric acid solution and the sulfuric acid solution having the hydrofluoric acid concentration of 1000 ppm was used, the silicon oxide film (SiO₂) and the silicon nitride film (SiN) were undesirably etched and removed. In other words, there is a risk of damage to the silicon oxide films (SiO₂) and the silicon nitride films (SiN) in the case where an organic substance such as a resist is removed using only the sulfuric acid solution to which hydrofluoric acid is added.

Also, according to experiments performed by the inventors, it was ascertained that the resist having the altered layer formed in the surface thereof cannot be removed in the case where the sulfuric acid solution to which hydrofluoric acid is added is used. In other words, it was ascertained that the sulfuric acid solution to which hydrofluoric acid is added is unsuitable for removing the resist.

Conversely, in the case where the oxidizing solution to which hydrofluoric acid was added (in this experiment, the oxidizing solution having the hydrofluoric acid concentration of 1000 ppm) was used, the silicon nitride film (SiN) was slightly etched and removed, but the etching and removal of the silicon oxide film (SiO₂) was suppressed. Further, the resist having the altered layer formed in the surface thereof was removed without peeling remnants (residue).

Therefore, by using an oxidizing solution to which hydrofluoric acid is added as the cleaning liquid, a resist having an altered layer formed in the surface thereof, which is conventionally difficult to remove, can be removed without leaving peeling remnants (residue) and without damaging the silicon oxide films (SiO₂) and the silicon nitride films (SiN).

Conventionally, it is necessary to remove the altered layer of the resist surface by ashing with dry etching and subsequently removing the remaining resist by performing processing using an SPM solution. Therefore, this leads to more processing processes, more types of processing apparatuses, longer processing times, etc. Conversely, by using an oxidizing solution to which hydrofluoric acid is added as the cleaning liquid, the resist having the altered layer formed in the surface thereof can be removed by one type of processing. Therefore, the productivity can be increased, production costs can be reduced, etc.

Although the case is illustrated in this embodiment where hydrofluoric acid is added to the oxidizing solution beforehand, the removal of the resist, etc., can also be performed by, for example, supplying the oxidizing solution and the hydrofluoric acid to the surface of the object W to be cleaned sequentially or substantially simultaneously. The removal may be performed not only on a resist having an altered layer formed in the surface thereof but also on a resist having no altered layer in the surface thereof. However, it is particularly useful to remove a resist having an altered layer formed in the surface thereof, which conventionally is difficult to remove.

A cleaning method according to this embodiment will now be described.

FIG. 4 is a flowchart illustrating the cleaning method. First, an oxidizing solution including oxidizing substances (e.g., peroxomonosulfuric acid and peroxodisulfuric acid) is produced by electrolyzing a sulfuric acid solution (step S1-1). In such a case, the oxidizing substances can be produced efficiently by making the sulfuric acid concentration of the sulfuric acid solution not less than 30 weight percent and not more than 70 weight percent.

Then, the temperature of the produced oxidizing solution is adjusted (step S1-2). Although such a temperature adjustment is not always necessary, considering the shortening of the processing time, the allowable temperature and strength of the cleaning system, etc., it is favorable to adjust the temperature of the oxidizing solution to be not less than 100° C. and not more than 110° C. The temperature adjustment can be performed on any of the produced oxidizing solution, the oxidizing solution during production (during the electrolysis), and the sulfuric acid solution supplied for the electrolysis.

The temperature of the hydrofluoric acid is adjusted (step S2). Although such a temperature adjustment is not always necessary, considering the shortening of the processing time, the allowable temperature and strength of the cleaning system, etc., it is favorable for the temperature of the hydrofluoric acid to be adjusted to be not less than 100° C. and not more than 110° C.

Then, the hydrofluoric acid and the oxidizing solution are supplied to the surface of the object W to be cleaned sequentially or substantially simultaneously (step S3). The supplying may be performed from a dispense unit and the like for each of the objects W to be cleaned and by sequentially immersing in the hydrofluoric acid and the oxidizing solution. Also, for example, the supplying may be performed sequentially or substantially simultaneously from separate piping systems for the hydrofluoric acid and the oxidizing solution. So-called single wafer processing, batch processing, and the like may be used.

FIG. 5 is a flowchart illustrating a cleaning method according to another embodiment.

In this embodiment, the oxidizing solution and the hydrofluoric acid are mixed; and the mixture is supplied to the surface of the object W to be cleaned.

First, an oxidizing solution including oxidizing substances (e.g., peroxomonosulfuric acid and peroxodisulfuric acid) is produced by electrolyzing a sulfuric acid solution (step S10). In such a case, the oxidizing substances can be produced efficiently by making the sulfuric acid concentration of the sulfuric acid solution not less than 30 weight percent and not more than 70 weight percent.

Then, the oxidizing solution and the hydrofluoric acid are mixed to produce a cleaning liquid (step S11). At this time, the hydrofluoric acid concentration and the amount of the oxidizing substances in the cleaning liquid are appropriately adjusted.

Continuing, the temperature of the produced cleaning liquid is adjusted (step S12). Although such a temperature adjustment is not always necessary, considering the shortening of the processing time and the allowable temperature and strength of the cleaning system, etc., it is favorable for the temperature of the cleaning liquid to be adjusted to be not less than 100° C. and not more than 110° C. The temperature adjustment can be performed on the oxidizing solution and the hydrofluoric acid prior to mixing.

Then, the cleaning liquid (the mixed liquid of the hydrofluoric acid and the oxidizing solution) is supplied to the surface of the object W to be cleaned (step S13). The supplying may be performed from a dispense unit and the like for each of the objects W to be cleaned and by immersing in the cleaning liquid. So-called single wafer processing, batch processing, and the like may be used.

Although the case is illustrated in FIG. 5 where the hydrofluoric acid is added to the oxidizing solution including the oxidizing substances after the oxidizing solution is produced, the hydrofluoric acid may be added to the sulfuric acid solution, which is the source material of the oxidizing solution; and then this solution may be electrolyzed to produce the cleaning liquid including oxidizing substances and to which hydrofluoric acid is added (referring to FIG. 6).

Also, the cleaning liquid may be produced by producing the oxidizing solution (the SPM solution) including the oxidizing substances by mixing a sulfuric acid solution and aqueous hydrogen peroxide and adding hydrofluoric acid thereto. Moreover, the cleaning liquid including oxidizing substances and having hydrofluoric acid added thereto may be produced by mixing a sulfuric acid solution, aqueous hydrogen peroxide, and hydrofluoric acid.

In other words, it is sufficient for the cleaning liquid to be a solution exhibiting acidity and including an oxidizing substance and hydrofluoric acid. The manufacturing method thereof may include adding the hydrofluoric acid after producing the acidic solution (the oxidizing solution) including the oxidizing substance or producing the oxidizing substance from a sulfuric acid solution having the hydrofluoric acid added thereto.

FIG. 6 is a schematic view illustrating a cleaning system in which a sulfuric acid solution having hydrofluoric acid added thereto is electrolyzed.

As illustrated in FIG. 6, the hydrofluoric acid supply unit 50 includes the tank 51 which retains hydrofluoric acid, the pump 52, and the open/shut valve 71. The tank 51, the pump 52, and the open/shut valve 71 are connected to a piping line on the sulfuric acid supply unit 15 side via the piping line 53 a. In other words, a piping line 53 a is connected to the piping line on the downstream side of the open/shut valve 70. The hydrofluoric acid retained in the tank 51 can be supplied to the anode chamber 30 of the sulfuric acid electrolysis unit 10 via the piping line 53 a by the operation of the pump 52. In other words, the hydrofluoric acid supply unit 50 has a function of supplying the hydrofluoric acid retained in the tank 51 to the anode chamber 30 of the sulfuric acid electrolysis unit 10; and a cleaning liquid including an oxidizing substance and having hydrofluoric acid added thereto can be produced by electrolyzing the sulfuric acid solution having the hydrofluoric acid added thereto.

Considering the addition of the hydrofluoric acid, it is favorable for at least the anode conductive film 35 to be made of a conductive diamond film.

A method for manufacturing a microstructure according to this embodiment will now be described.

Examples of a method for manufacturing a microstructure include, for example, a method for manufacturing a semiconductor device. Here, the manufacturing processes of the semiconductor device include the so-called front-end processes such as the processes that form a pattern on a substrate (wafer) surface by film formation, resist coating, exposing, developing, etching, resist removal, etc., the inspection processes, cleaning processes, heat treatment processes, impurity introduction processes, diffusion processes, planarizing processes, etc. The so-called back-end processes include the assembly processes of dicing, mounting, bonding, encapsulation, etc., the functional and reliability inspection processes, etc.

In such a case, the removability of the resist can be increased by using, for example, the cleaning liquids, the cleaning methods, and the cleaning systems described above during the resist removal process. In particular, a resist having an altered layer formed in the surface thereof, which is conventionally difficult to remove, can be removed without leaving peeling remnants (residue) and without damaging the silicon oxide films (SiO₂) and the silicon nitride films (SiN).

Conventionally, it is necessary to remove the altered layer of the resist surface by ashing with dry etching and subsequently removing the remaining resist by performing processing using an SPM solution. Therefore, this leads to more processing processes, more types of processing apparatuses, longer processing times, etc. Conversely, by using the cleaning liquids, the cleaning methods, and the cleaning systems described above, the resist having the altered layer formed in the surface thereof can be removed by one type of processing. Therefore, the productivity can be increased, production costs can be reduced, etc.

Known technology may be applied to the processes other than those of the cleaning methods and the cleaning systems according to this embodiment described above, and therefore a detailed description thereof is omitted.

Although a method for manufacturing a semiconductor device is illustrated as one example of the method for manufacturing the microstructure, the method for manufacturing the microstructure is not limited thereto. For example, applications are possible in fields such as liquid crystal display devices, phase shift masks, micromachines in MEMS fields, precision optical components, etc.

In the cleaning system described above, it is not always necessary to provide a configuration to circulate the solution. As illustrated in FIG. 7, the solution used in the cleaning processing unit 12 may be recovered into the returning tank 63 with contaminants and the like and then discharged to the outside of the system via the discharge piping line 75.

Such processing may be used not only to remove a resist made of an organic substance, but also to similarly remove metal impurities, particles, and dry etching residue, etc.

For example, during the patterning of metal interconnects with large aspect ratios, many interconnection metals, oxides and halides of the interconnection metals, barrier metals, oxides and halides of the barrier metals, etc., are deposited. Also, during the patterning of a silicon system having a large aspect ratio, many silicon oxides and halides are deposited. In many cases, such substances cannot be removed only by the oxidizing capability of the oxidizing substances of an SPM solution.

However, many of such deposits can be decomposed and removed by hydrofluoric acid. By using the cleaning liquids, the cleaning methods, and the cleaning systems described above, such removal is possible without damaging the silicon oxide films (SiO₂) and the silicon nitride films (SiN).

In other words, many applications are possible when removing contaminants adhered to a microstructure. In such a case, it is particularly useful when oxides and nitrides are on the surface because the contaminants can be removed while suppressing the removal of the oxides and the nitrides.

A robot may be provided to transfer the object to be cleaned. Each of the tank 60 retaining the sulfuric acid solution and the tank 51 retaining the hydrofluoric acid may be connected to a line of a factory to automatically replenish the solution. A rinse bath may be provided for rinsing the object to be cleaned after removing the contaminants. Such a rinse bath may include an overflow control device and a temperature control device using an in-line heater. It is suitable to use quartz as the material of the rinse bath.

Hereinabove, embodiments are illustrated. However, the invention is not limited to the descriptions thereof.

Design modifications appropriately made by one skilled in the art in regard to the embodiments described above also are included in the scope of the invention to the extent that features of the invention are included.

For example, the configurations, dimensions, material qualities, dispositions, etc., of the components of the cleaning systems described above are not limited to those illustrated herein and may be appropriately modified.

Further, the components of the embodiments described above may be combined within the extent of feasibility; and such combinations also are included in the scope of the invention to the extent that the features of the invention are included.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel liquids, cleaning methods, cleaning systems and manufacturing methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the liquids, cleaning methods, cleaning systems and manufacturing methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention. 

1. A cleaning liquid, comprising an oxidizing substance and hydrofluoric acid and exhibiting acidity.
 2. The cleaning liquid according to claim 1, wherein the oxidizing substance includes at least one selected from peroxomonosulfuric acid and peroxodisulfuric acid.
 3. The cleaning liquid according to claim 1, wherein the oxidizing substance is produced by one selected from electrolyzing a sulfuric acid solution, electrolyzing hydrofluoric acid added to a sulfuric acid solution, and mixing a sulfuric acid solution with aqueous hydrogen peroxide.
 4. A cleaning method, comprising producing an oxidizing solution including an oxidizing substance by one selected from electrolyzing a sulfuric acid solution, electrolyzing hydrofluoric acid added to a sulfuric acid solution, and mixing a sulfuric acid solution with aqueous hydrogen peroxide, and supplying the oxidizing solution and hydrofluoric acid to a surface of an object to be cleaned.
 5. The method according to claim 4, wherein a sulfuric acid concentration of the sulfuric acid solution is not less than 30 weight percent and not more than 70 weight percent.
 6. The method according to claim 4, wherein the oxidizing substance includes at least one selected from peroxomonosulfuric acid and peroxodisulfuric acid.
 7. The method according to claim 4, wherein at least one selected from a temperature of the oxidizing solution and a temperature of the hydrofluoric acid is not less than 100° C. and not more than 110° C.
 8. The method according to claim 4, wherein the oxidizing solution is supplied to the surface of the object to be cleaned sequentially or substantially simultaneously with the hydrofluoric acid.
 9. The method according to claim 4, wherein the oxidizing solution and the hydrofluoric acid are mixed, and the mixed solution is supplied to the surface of the object to be cleaned.
 10. The method according to claim 9, wherein a temperature of the mixed solution is not less than 100° C. and not more than 110° C.
 11. A cleaning system, comprising: a sulfuric acid electrolysis unit including an anode, a cathode, a partitioning membrane provided between the anode and the cathode, an anode chamber provided between the anode and the partitioning membrane, and a cathode chamber provided between the cathode and the partitioning membrane, the sulfuric acid electrolysis unit electrolyzing a sulfuric acid solution to produce an oxidizing substance in the anode chamber; a sulfuric acid supply unit supplying a sulfuric acid solution to the anode chamber and the cathode chamber; a cleaning processing unit performing a cleaning processing of an object to be cleaned; a first hydrofluoric acid supply unit supplying hydrofluoric acid to the cleaning processing unit; and an oxidizing solution supply unit supplying an oxidizing solution including the oxidizing substance to the cleaning processing unit.
 12. The system according to claim 11, wherein the first hydrofluoric acid supply unit supplies the hydrofluoric acid to the cleaning processing unit sequentially or substantially simultaneously with the oxidizing solution supplied by the oxidizing solution supply unit.
 13. The system according to claim 11, further comprising a mixing unit to mix the hydrofluoric acid supplied by the first hydrofluoric acid supply unit with the oxidizing solution supplied by the oxidizing solution supply unit.
 14. The system according to claim 11, further comprising a solution circulation unit recovering at least one selected from the oxidizing solution and the hydrofluoric acid discharged from the cleaning processing unit and resupplying the at least one to the cleaning processing unit.
 15. The system according to claim 14, wherein the solution circulation unit includes a heater to perform a temperature control of the oxidizing solution.
 16. The system according to claim 11, wherein at least one selected from the anode and the cathode includes a conductive diamond film formed on a surface of a conductive base member.
 17. A cleaning system, comprising: a sulfuric acid electrolysis unit including an anode, a cathode, a partitioning membrane provided between the anode and the cathode, an anode chamber provided between the anode and the partitioning membrane, and a cathode chamber provided between the cathode and the partitioning membrane, the sulfuric acid electrolysis unit electrolyzing a sulfuric acid solution to produce an oxidizing substance in the anode chamber; a sulfuric acid supply unit supplying a sulfuric acid solution to the anode chamber and the cathode chamber; a cleaning processing unit performing a cleaning processing of an object to be cleaned; a second hydrofluoric acid supply unit supplying hydrofluoric acid to the anode chamber; and an oxidizing solution supply unit supplying an oxidizing solution including the oxidizing substance to the cleaning processing unit.
 18. The system according to claim 17, further comprising a solution circulation unit recovering at least one selected from the oxidizing solution and the hydrofluoric acid discharged from the cleaning processing unit and resupplying the at least one to the cleaning processing unit.
 19. The system according to claim 17, wherein at least one selected from the anode and the cathode includes a conductive diamond film formed on a surface of a conductive base member.
 20. A method for manufacturing a microstructure, comprising cleaning an object to be cleaned by a cleaning method and forming a microstructure, the cleaning method including producing an oxidizing solution including an oxidizing substance by one selected from electrolyzing a sulfuric acid solution, electrolyzing hydrofluoric acid added to a sulfuric acid solution, and mixing a sulfuric acid solution with aqueous hydrogen peroxide, and supplying the oxidizing solution and hydrofluoric acid to a surface of an object to be cleaned. 